A worker at Japan's wrecked nuclear power plant died after the hatch at the back of a truck closed on his head Saturday, the latest mishap at a complex still struggling with the cleanup from the 2011 Fukushima disaster.

The operator of the Fukushima Dai-ichi plant said the 52-year-old man was rushed to a nearby hospital but was pronounced dead soon after.

A man who was working with the victim told plant officials that he found him slumped at the back of a 7.9-meter-long (32-foot) tank truck used to transport underground water and dirt dug from a frozen wall construction site to a dump site, according to the operator, Tokyo Electric Power Co.

The co-worker told TEPCO officials that minutes before the incident, the victim indicated to him that he had finished cleaning and inspecting the truck's tank and wanted him to close the hatch, TEPCO spokesman Shinichi Nakakuki said.

The co-worker said he then closed the hatch using a lever behind the driver's compartment. Officials said that he most likely could not see his partner at the back of the truck from that position.

Difficulties

The workers' full-face masks and helmets make it difficult to communicate.

There were no other workers present at the site of the incident.

TEPCO officials said they did not know why the victim could not escape when the hatch started coming down, or whether any screaming was heard.

Police are investigating the incident, said TEPCO, which did not disclose the victim's name.

The decades-long decommissioning of the plant, which was wrecked in the March 2011 earthquake and tsunami that devastated northeastern Japan, involves thousands of workers.

The number of accidents last year, including injuries and sickness, doubled to 64 from a year earlier. Saturday's death, the second this year, occurred weeks after the government and TEPCO announced plans to slow down projects to improve safety. In January, a worker died after accidentally falling from atop a storage tank.

The two men involved in Saturday's incident were assigned to the truck used at the site where a frozen underground wall is being installed near highly contaminated reactor buildings, a project aimed at curbing a contaminated water problem hampering the decommissioning of the plant.